The present invention generally relates to a color printing technique, and more particularly a color simulating technique for calibrating, controlling and estimating a color print image with the aid of a color image displayed on a screen of a color monitor. In such a color printing simulation at first a set of primary color signals of cyan, magenta, yellow and black are derived by scanning a set of color separation films of cyan, magenta, yellow and black by means of a cathode ray tube scanner or a color television camera. Next the primary color signals are processed in accordance with given equations to produce three additive primary color signals of red, green and blue, and then the primary color signals thus produced are supplied to a color monitor so as to display a color image on its screen.
While inspecting the color image displayed on the monitor screen, accurate perception of color reproduction quality, preproof study of color images, inspection of color balance, etc. can be effected and the simulation of color printing process can be carried out.
There have been developed several methods for reproducing color and among them a color reproducing method on the basis of Neugebauer equations relating to the color reproducibility for halftone is most accurate and practical. The color reproducing method based on the Neugebauer theory can be realized in various ways in accordance with methods of expressing theoretical equations and manners for processing signals. For instance, in a method described in Japanese Patent application Publication Nos. 4,777/76 and 5,305/76, four color separation films of cyan, magenta, yellow and black are scanned by a cathode ray tube scanner to derive color image signals and then these color image signals are processed to produce four primary color signals of cyan, magenta, yellow and black, three secondary color signals of red, green and blue, a tertiary color signal and a signal for representing color of papers to be used. These nine signals are then multiplied by suitable coefficients which differ for inks and papers to be used and other elements as well as for three stimulative values of a color video image reproduced on a monitor screen. Finally these signals are totally summed up for respective stimulative values. In this method in order to produce the above mentioned nine signals there must be provided eight logarithmic conversion circuits, nine summing circuits and nine exponential amplifiers or twenty four multiplying circuits. As compared with the summing circuit, the multiplying circuit is much more complicated and is liable to generate error and thus, it is preferable to reduce the number of the multiplying circuits. It should be further noted that in the known methods since the number of elements to be adjusted is large, it is rather difficult to correct or adjust the colors of the displayed image in a simple and accurate manner.